The ability to maintain a latent image is of paramount importance to commercial photographic products. Customers typically make exposures on a roll of film over a period of time which can range up to several months from the first to the last exposure. These latent images are then processed together and should produce dye densities in color film independent of exposure age for optimum color reproduction. Complete maintainence of the latent image under these conditions is rarely achieved in the complex chemical milleau consitituting a color film. Rather, ways have been sought to minimize its loss and thereby deliver to the customer the most consistent color reproduction possible.
A variety of latent image stabilizers have been described (Herz, U.S. Pat. No. 4,374,196) with notable success achieved by derivatives of N-2-alkynylaminobenzoxazolium salts (Lok et al, U.S. Pat. No. 4,451,557 and U.S. Pat. No. 4,378,426 and Eikenberry et al, U.S. Pat. No. 5,500,333). Although these materials showed good success in reducing latent image loss, they were examined in single color, single layer formats considerably simpler than the complex, tri-color, multi-layer format needed for complete and accurate color reproduction.
The translation of single layer latent image stability to multi-layer performance is often frustrated by unexpected offsets and chemical interactions. Furthermore, a multi-layer format will evolve during the development of a new commercial film for a variety of reasons: to gain improved color reproduction through inter-image effects; to improve the chemical stability prior to exposure; to reduce sensitivity to variable processing factors; or for a variety of other reasons. This evolution usually involves a shift in the chemical and/or physical make up of the multi-layer film that brings with it a change in the requirements needed to obtain latent image stability. For example, a combination of emulsion and addenda that gave good performance in a single layer or in the initial multi-layer format may prove insufficient as the format evolves.